The present invention relates to a method for testing an electric motor which is used to, for example, actuate a subsea valve. More specifically, the invention relates to a method for testing the operability of such a motor without actuating the valve.
Subsea installations often include a number of valves for controlling the flow of fluids through certain of their components. These subsea valves are normally hydraulically actuated, since hydraulic actuators are traditionally regarded as being fairly reliable. However, current hydraulic actuators are practically limited in the depths at which they can be used. In contrast, electric actuators are not so limited. Thus, by replacing current hydraulic actuators with electric actuators, such as electric motors, subsea installations can be located at greater depths and can thus potentially experience large cost savings. However, while electric actuators are common in many industries, they are not often used in subsea installations. This is due mainly to reliability concerns, since a failure of a subsea valve can potentially lead to environmental disasters.
Hydraulically actuated subsea valves are normally tested by opening and closing the valves. To do this the subsea installation must be shut down; but since these valves are usually only tested once per year, this is not regarded as a problem. The hydraulic actuators themselves are not specifically tested since they are regarded as very reliable.
However, electric actuators do need to be tested since their electric motors are considered to be less reliable than hydraulic actuators. Due to these reliability concerns, an operator may desire to test the electric motors relatively frequently to ensure that they will perform as intended. Therefore, the testing of the electric motors should ideally not affect the valves to which they are connected to avoid having to shut down the subsea installation.